A continuous rpm and torque conversion requires high transfer efficiencies especially in automotive applications.
Belt arrangements known to date for transmitting rotational movements between at least two belt pulleys comprise two endless load carriers and a plurality of blocks mounted thereon. In this connection, reference can be made to, for example, European patent publication 0,135,710 and U.S. Pat. Nos. 4,734,085 and 5,776,023. In the known belt arrangements, the load carriers are fitted into slots which run from inclined side surfaces of the blocks toward the center regions thereof. The load carriers as well as the slots for accommodating the same have convex or concave sections whereby a relatively immovable interlocking engagement results in the longitudinal direction of the load carriers. The convex or concave sections are arranged on the load carriers and the blocks transversely to the running direction. With the aid of these sections, a synchronism between the forward movement of the load carriers and the blocks is obtained.
Different running radii occur at the drive end and output end in friction-tight operating V-belt drives and these different radii are caused by the system. In this way, curvature changes and stress changes occur in the body of the belt during operation. Different contact conditions occur at the contact location between the support blocks and the load carrier depending upon the running radius. These contact conditions have not been optimized in a targeted manner up to now in belt configurations for transmitting high powers with a continuously adjustable rpm ratio between drive shaft and output shaft. These belts are made of load carriers having elastomer cords and possibly fabric as well as a plurality of support blocks made of one material or a combination of materials with a higher modulus of elasticity than the elastomer used.
The different contact conditions occur because the load carrier, which consists in large parts of elastomer, is practically incompressible and is, because of the support blocks in the direction transverse to the belt, hindered to deflect in this direction. The direction transverse to the belt is in the direction of the transmission shaft axes. Depending upon the adjusted running radius, the arcuate length changes as the length, which is available for the elastomer beneath the cords, and, with reducing radius, more expansion space must be provided in the radial direction for the incompressible elastomer to an increasing extent. The configuration of a radius on the support block and a radius on the load carrier is known. The radius, which is configured on the support block is greater or equal to the radius on the load carrier as disclosed in U.S. Pat. No. 4,734,085. The opposite case is shown in U.S. Pat. No. 5,776,023.
It is an object of the invention to optimize the contact conditions between the load carrier and the blocks. The application of pressure is reduced where sliding movements occur in order to minimize losses and to increase efficiency.
The V-belt of the invention is wound around at least two pulleys each defining a groove and includes: at least one load carrier defining a longitudinal axis and being movable in the direction of the axis; a plurality of blocks having respective slots in which the load carrier is fitted; the load carrier being made of an elastomer and a plurality of tension cords; each of the blocks being disposed transversely to the longitudinal axis and having inclined surfaces adapted to the groove; each of the slots extending from one of the inclined surfaces of the block corresponding thereto toward the center region thereof; each of the blocks and the load carrier being interlocked so as to be immovable relative to each other in the direction of the longitudinal axis while, at the same time, being releasable from each other in a direction transverse to the longitudinal axis; each of the slots having mutually adjacent boundary surfaces between which the load carrier is fitted; the load carrier having respective contact surfaces facing toward corresponding ones of the boundary surfaces; the load carrier having convex and/or concave sections on at least one of the contact surfaces and the slot of each block having convex and/or concave sections on at least one of the boundary surfaces; the sections of the boundary surfaces coming into interlocking engagement with the concave or convex sections of the at least one contact surface; the contact surface and the boundary surface conjointly defining a contact region which is assumed from the stretched state of the V-belt to the state thereof wherein the smallest running radius occurs; and, over the complete extent of the contact region, a continuously changeable curvature or a composite of at least three sections of constant curvature is being realized on one of the contact partners in such a manner that the curvature from the center of the contact region to the outer regions thereof increases.
The force transmission between the load carrier and the support block is improved in that, on at least one contact partner, a continuously changing curvature or a composite of at least three sections of constant curvature are realized in such a manner that the curvature increases from the center of the contact region toward the outer regions. The contact region is from the stretched condition of the belt to the condition of smallest running radius.
The contact between the load carrier and the support block includes, in part, a form-tight configuration and, in part, a force-tight configuration. When the running radius becomes less, the above-described displacement action on the incompressible load carrier increases so that the form-tight connection is increased in the outer region with increasing curvature with surface normal peripheral forces. On the other hand, with the displacement effect, an increase of the surface pressure concentrates in the region of the larger radius at the center of the contact region so that, at this location, larger surface tangential thrust forces operate primarily in the peripheral direction with the friction value present between the load carrier and the support block; whereas, the pressing and the radially directed friction forces in the side regions are reduced in favor of the form-tight connection.
Up to now, the largest relative movements between the surfaces have occurred in the outer region in the change from stretched segment to curved segment between the discs. For this reason, the efficiency of the force transfer is improved via a reduction of the friction forces in the regions of greater movement and especially for the transfer ratios with small running radii.
Preferably, at least one load carrier is surrounded by a cover fabric at least one of the contact surfaces to the slot flanks (boundary surfaces of the slot). Such a cover fabric protects generally the base body of the belt against wear in the presence of relative movements and especially in the peripheral regions of the contact zone between load carrier and support block where the problem of slide movements is the greatest.